A turbocompressor typically has at least three compressor stages each in turn having a housing part forming a io respective gas intake and a housing part forming a respective gas output. Each stage further has a respective impeller or fan carried on a common shaft structure to form a rotor supported by radial and axial bearings in the housing parts forming the intakes and outputs.
In radial turbocompressors, the gas flows axially into the impeller of the first stage. It is collected in the impeller intake and diverted radially and accelerated by its vanes. The gas leaves the impeller chambers at great velocity at the impeller circumference and flows into an expanding, radial diffusor. Here its speed is sharply reduced. The kinetic energy is converted to pressure. Finally the gas that has been compressed and heated in this manner is conducted in a spiral collection housing to an output connector.
High pressures can be produced by providing a plurality of impellers in succession along a drive shaft. The impellers are operated at the same speed. Together with the shafts they form a rotor having a common mount and drive. The radial bearings for such single-shaft radial turbocompressors are generally arranged on the shaft ends. The axial bearing is also positioned on a shaft end so that the rotor can move only io axially.
The housing of such turbocompressors is either divided axially or has an integrated outer housing cover. In an axially divided embodiment, the rotor is enclosed by a lower housing half and an upper housing half. In order to make the rotor accessible, the entire upper housing part must be removed. The upper and lower housing halves are each cast or welded in a single piece. In another embodiment, the housing has an integral cylindrical outer housing shell that is cast or welded and parts, such as for instance intakes and outputs for the individual compressor stages, are each divided axially so that they can be mounted between the impellers.
After cooling and passing through some ducts, the gas compressed in the first impeller is conducted to the second impeller and from there, after further cooling, to the next impeller. The goal is to bring the multistage gas compression as close as possible to the ideal, isothermic compression process.
In multistage turbocompressors, hot and cold housing parts are arranged successively in a fixed relationship. Since the cold and hot housing parts are always securely mounted to, welded to, or cast with one another, there is internal stress in the housing due to the thermal expansion. The different temperatures of the individual housing parts cause different amounts of thermal expansion for the parts. There may also be pressure deformations in the housing parts.
During operation, the arrangement of the bearings on the shaft ends and the axial division of the housing with housing parts that are securely joined to one another or the internal housing parts gripped in a common housing cover can lead to a reduction in the clearances between the impellers and the housing parts adjacent to them. This can lead to the impellers scraping against the housing and thus to damage to the turbocompressor.